1. Field of the Invention
This invention relates generally to the field of mechanisms adapted to transmit or absorb power and more particularly to devices adapted to transmit or absorb variable amounts of power by delivering an incompressible fluid in varying quantities within a range of quantities and devices adapted to deliver a variable quantity of an incompressible fluid at a desired pressure.
2. Prior Art
In connection with the operation of vehicles, particularly commercial vehicles powered by internal combustion engines, a number of problems are presented with respect to engine cooling, to the supply of variable quantities of incompressible fluids, such as lubricating oil, and to the efficient braking of the vehicle of accessory loads driven by the engine.
Considering first the problem of engine cooling, it has long been common to provide a heat exchanger in the form of a radiator comprising finned tubes through which air may be passed to dissipate heat from an engine cooling system or oil cooling system. It is also common to provide a fan, normally driven directly or by a belt from the engine crankshaft, to induce a flow of air through the radiator. Such a fan consumes a substantial amount of power, the quantity of power being a function of the rotational speed at which the fan is driven. In the case of a fan driven directly by a vehicle engine it is apparent that the speed of the fan will be proportional to the engine speed. During operation over the highway, the vehicle speed will also generally be proportional to the engine speed (for any particular gear ratio). However, as the vehicle speed increases, the ram effect of the vehicle will increase the flow of air through the radiator and the requirement for the fan decreases. Thus it is apparent that much of the power delivered to drive the fan of a vehicle engine may be wasted during normal operation of the vehicle. Since such a fan may consume upwards of 20 or 25 horsepower, the quantity of energy involved is significant. Accordingly, it is an object of the present invention to provide a variable power fan drive in which the power or torque supplied to the fan is varied to meet the actual cooling requirements of the engine. In another aspect of the invention, a control means is provided whereby the power delivered to the fan through the fan drive is limited to be only slightly greater than that required to drive the fan at whatever speed the fan may be operating. Thus the fan may be accelerated smoothly to the required operating speed. A still further aspect of the invention involves the limitation of the torque to a predetermined maximum value.
Turning next to the problem of supplying fluids, such as oil, to a vehicle engine or its auxiliaries, it is common to utilize mechanisms such as positive displacement gear pumps to provide a supply of engine lubricating oil to lubricate the engine or drive auxiliaries such as hydraulic lifts or power take-off devices. Again, where the gear pump is directly driven from the engine, the quantity of the oil supplied varies with the speed of the engine. In order to provide a sufficient quantity of oil to meet the engine or accessory requirements at low speeds, the gear pump must be designed so that excess quantities of pressurized oil are provided when the engine is operated at normal or high speeds. Such excess quantities of pressurized oil are frequently by-passed back to a sump so that a substantial amount of energy is wasted in pumping the oil through the oil pressurizing system. It is therefore another object of the present invention to provide a mechanism capable of supplying an incompressible fluid at any desired flow rate whereby the energy required for pumping and pressurizing the fluid is limited to the actual needs of the system.
Finally, it is well known that large commercial vehicles operating at normal highway speeds possess a very large momentum and that it is difficult to brake such vehicles using the ordinary drum or disc-type friction brakes without unduly shortening the life of such drum or disc brakes. As a partial solution for adequate braking, it is common for such vehicles to utilize the compression braking power of the engine by operating the vehicle in a lower gear during descent of long hills. In addition, many commercial vehicles are provided with engine retarders which make more effective use of the engine compression by opening the engine exhaust valves out of the normal sequence whereby the energy required to compress air in the engine cylinders is not recovered in the subsequent expansion stroke of the engine. Additionally, such vehicles may be provided with exhaust brakes which increase the exhaust manifold pressure. Another device which has been used is the electrodynamic brake by which the mechanical energy of the vehicle is transformed into electrical energy which is dissipated through resistance elements. In accordance with another aspect of the present invention, a mechanical device is provided wherein a variable ratio of compressible and incompressible fluids is introduced into the device and whereby the power absorbed by the device is a function of the proportion of the incompressible fluid passing through the device. In this manner the device of the present invention functions as a power absorbing or braking or retarding device to provide a primary or auxiliary source of braking power.
While the primary utility of the device lies in its application to commercial vehicles, it will be appreciated that the device is also applicable to stationary engines or to rotating equipment such as turbines or blowers which may require a braking function, a power transmission function, or a variable supply of an incompressible fluid such as fuel or oil.